Water intake riser

ABSTRACT

A water intake riser that can be suspended from a vessel having a riser connected to a riser hanger, which riser hanger includes a first tubular element, a second tubular element to which the riser is connected, a flexible load transfer element joining the tubular elements, and a hose of which the ends are secured to the adjacent ends of the tubular elements.

The present invention relates to a water intake riser. Such a waterintake riser is used on a vessel to provide cooling water to a heatexchanger. In particular such a water intake riser is used on a vesselon which a plant for liquefying natural gas is arranged. In thespecification and in the claims the word vessel is used to refer to aship, a barge, a floating platform and so on.

An example of such a riser is described in the article by R Franciss,Maximum stress model test of a seawater lift casing to a Petrobras PXXVplatform in Albacora field, presented at 9th International symposium onOffshore Engineering, September 1995. The paper describes a floatingoffshore platform provided with water intake risers that are hingeablyconnected to the submerged pontoons of the platform.

It is an object of the present invention to provide a water intake riserhaving a simple and reliable design.

To this end the water intake riser that can be suspended from a vesselaccording to the present invention comprises a riser connected to ariser hanger, which riser hanger comprises a first tubular element, asecond tubular element to which the riser is connected, a flexible loadtransfer element joining the tubular elements, and a hose of which theends are secured to the adjacent ends of the tubular elements.

The invention further relates to a vessel provided with a water intakeriser.

The invention will now be described by way of example with reference tothe accompanying drawings, wherein

FIG. 1 shows schematically and not to scale a partial longitudinalsection of the water intake riser according to the present invention;

FIG. 2 shows a section along line II-II of FIG. 1;

FIG. 3 shows schematically and not to scale a cross-section of thebottom of a vessel provided with three water intake risers according tothe present invention; and

FIG. 4 shows schematically and on a larger scale detail IV of FIG. 3.

Reference is now made to FIG. 1 showing schematically and not to scalethe water intake riser 1 according to the present invention. The waterintake riser 1 is suspended from a hull 2 of a vessel (not shown). Thewater intake riser 1 comprises an elongated tube 3 connected to a riserhanger 4. The riser hanger 4 comprises two tubular elements, a firsttubular element 6 and a second tubular element 7. The upper end part ofthe first tubular element 6 has an open end provided with a suspensionridge 8. The suspension ridge 8 matches with a suitably formed opening10 in the hull 2 so that the first tubular element 6 is supported in theopening 10, and thus secured to the vessel. Securing the first tubularelement 6 to the vessel (not shown) allows suspending the water intakeriser 1 from the hull 2.

The riser hanger 4 further comprises a second tubular element 7. Theupper end of the elongated tube 3 is connected to the lower end of thesecond tubular element 7 by any suitable means. In FIG. 1 the diameterof the connection is larger than the diameter of the opening 10.However, suitably, the diameter of the opening 10 is so selected thatthe water intake riser can be lowered through it until the suspensionridge 8 is supported in the opening 10.

The riser hanger 4 further comprises a flexible load transfer element 16joining the tubular elements 6 and 7. In the embodiment shown in FIG. 1,the flexible load transfer element 16 is a chain. The riser hanger 4further comprises a hose 17 of which the ends are secured to theadjacent end parts 19 and 20 of the tubular elements 6 and 7. The hose17 is secured in a watertight way to the end parts 19 and 20.

Suitably, each tubular element 6 and 7 is provided with a cross-shapedinternal 22 (see also FIG. 2) having means 23 for securing the flexibleload transfer element to the internal 22. The cross-shaped internal 22is suitably welded to the inner surface of the tubular element 6 or 7.For the sake of simplicity the welds have not been shown.

In the water intake riser 1 of the present invention the hose 17 forms aconduit for water, whereas the flexible load transfer element 16transfers the self-weight and the dynamic loads of the elongated tube 3to the first tubular element 6. In this way the function of transferringwater is separated from transferring a load.

Reference is now made to FIG. 3. FIG. 3 shows the lower part of a vessel30 provided with at least two water intake risers. In this case thevessel 30 is provided with three water intake risers according to thepresent invention, wherein the first tubular element (not shown) issecured to the vessel 30 and suspended from the hull 2 as shown in moredetail in FIG. 1.

In order to prevent the water intake risers 1 from colliding, there isprovided at least one riser-spacer 35. The dynamic response of the waterintake risers 1 will determine the number and the positions of theriser-spacers 35. In FIG. 3 only one riser-spacer 35 is shown.

The riser-spacer 35 comprises interconnected guide sleeves 36, one guidesleeve 36 for each water intake riser 1. Bars 37 form theinterconnection. Each guide sleeve 36 defines an aperture 40 (see FIG.4), which aperture 40 allows the elongated tubes 3 to pass freelythrough it and allows limited rotation of the elongated tubes 3 about ahorizontal axis 43. The horizontal axis 43 is an axis that is lying in aplane of symmetry of the riser-spacer 35, which plane is perpendicularto the direction of passage through the aperture 40.

The riser-spacer 35 is suspended from the vessel 30 to a predetermineddepth. In the embodiment shown in FIG. 3, the riser-spacer 35 issuspended by means of a cable 45 secured in the hull 2. In analternative embodiment a chain replaces the cable 45, or one of theguide sleeves is secured to a water intake riser.

Suitably the length of the guide sleeve 36 is in the range of one tofour times the outer diameter of the riser. The bars 37 interconnectingthe guide sleeves 36 of the riser-spacer can be replaced by a frame orby a solid polygon. Suitably the thickness of the solid polygon isbetween three to four times the diameter of a riser in order to preventvortex shedding of the riser.

The open upper ends of the water intake risers 1 open into a receptacle46 inside the vessel 30 from which the water is withdrawn (not shown)for use as cooling water.

Suitably the number of water intake risers is between two and eight.

1. A water intake riser that can be suspended from a vessel comprising ariser connected to a riser hanger, which riser hanger comprises: a firsttubular element; a second tubular element to which the riser isconnected; a flexible load transfer element joining the tubularelements; and a hose of which the ends are secured to the adjacent endsof the tubular elements.
 2. The water intake riser according to claim 1,wherein each tubular element is provided with a cross-shaped internalhaving means for securing the flexible load transfer element to theinternal.
 3. The water intake riser according to claim 1, wherein theflexible load transfer element is a chain.
 4. A vessel provided with atleast one water intake riser that can be suspended from the vesselcomprising a riser connected to a riser hanger, which riser hangercomprises: a first tubular element; a second tubular element to whichthe riser is connected; a flexible load transfer element joining thetubular elements; and a hose of which the ends are secured to theadjacent ends of the tubular elements, wherein the first tubular elementis secured to the vessel.
 5. The vessel according to claim 4, which isprovided with at least two water intake risers and with at least oneriser-spacer comprising: interconnected guide sleeves; one guide sleevefor each riser; wherein each guide sleeve defines an aperture; whichaperture allows a riser to pass freely through it and allows limitedrotation of the riser about a horizontal axis; and wherein eachriser-spacer element is suspended from the vessel to a predetermineddepth.
 6. The vessel according to claim 5, wherein the number of waterintake risers is between two and eight.
 7. The vessel according to claim5, wherein the length of the guide sleeve is in the range of one to fourtimes the diameter of the riser.
 8. The vessel according to claim 4,wherein the hull of the vessel is provided with at least one opening forthe at least one water intake riser; and wherein an upper end of thefirst tubular element of the at least one water intake riser issupported in the opening.